The use and operation of impact sprinklers is well-known, as are a variety of design limitations and attendant issues. An impact sprinkler rotates in a full or partial circle to distribute water therefrom. A water stream is directed through a nozzle and against a deflector located on a rotation shaft. The water is radially distributed by rotation of the rotation shaft and deflector.
More specifically, the rotation shaft and deflector are periodically and incrementally rotated a short distance as a result of an impact. To permit this rotation, the rotation shaft is rotatably supported by the sprinkler. The water stream outwardly-deflected from the deflector strikes an arm or spoon formed on an impact disc, also rotatably supported by the sprinkler. The water striking the spoon forces the impact disc to rotate so that the spoon is shifted out of the path of the water stream, the shifting overcoming the bias of a spring resisting such movement and contributing to the support of the impact disc. Accordingly, such shifting causes the spring to store energy. Under desirable operating conditions, the water strikes the spoon to cause the impact disc to continue rotating a short distance beyond the water stream.
The spring forces the impact disc into the rotation shaft to cause the rotation of the rotation shaft. The impact disc rotating from the water stream causes a build-up of energy in the spring, and eventually the spring force slows and stops the impact arm, eventually forcing the impact disc to counter-rotate and return towards the water stream. The spoon re-enters the water stream approximately coincident with or shortly before a structure on the impact disc collides with structure on the rotation shaft. This collision causes the rotation shaft to rotate a short distance in the counter-rotation direction. In this manner, the water stream direction is rotationally re-positioned.
The angular amount of rotation of the rotation shaft is dependent on the magnitude of the collision, or the size of impact, between the structures of the impact arm and the rotation shaft. This collision itself is dependent on a number of factors.
For a nozzle providing a low flow speed or volume, the water stream striking the deflector and then the spoon will effect only a short or limited amount of rotational movement by the impact disc. Accordingly, the energy stored in the spring will be low, and the counter-rotation or return of the impact disc will be a similarly short distance. This results in the spoon or impact arm having a low dwell time and re-entering the water stream before a full emission stream pattern develops, thus shortening the throw distance for the sprinkler. The dwell time is generally the amount of time during which the spoon is not aligned with the water stream, and more specifically, the time during which the water stream is free to directly distribute water to the surrounding environment without interference by the spoon.
Additionally, this may result in insufficient rotation of the rotation shaft. A portion of the energy stored by the spring will be lost as the spoon re-enters the water stream, while the remainder will be transferred to the rotation shaft through the collision. The collision is resisted by a certain amount of static friction between the rotation shaft and its support by the sprinkler. If the energy stored by the spring is relatively low, the collision is consequently low also.
In some instances, the energy may not sufficiently rotate the rotation shaft. In such a case, the spoon merely oscillates in and out of the water making little or no collision.
Another problem is that the rotational force for deflecting the impact disc or arm out of the water stream may be excessive. This results in over-rotation of the impact disc, which itself may cause an impact between the impact disc and the rotation shaft in the rotation direction, consequently resulting in rotation of the direction of water stream emission in a direction opposite to that desired, this effect being referred to herein as back-impact.
Previous designs for impact sprinklers tend to suffer from one or more of the foregoing shortcomings. More specifically, dwell-time issues resulting from low water flow may be addressed by using a light spring (i.e., a spring having a low spring constant) for the impact disc. However, this may result in the over-rotation of the impact arm (reverse impact with rotation shaft) and/or insufficient energy stored in the spring arm for causing a forward impact with the rotation shaft. Additionally, the impact disc is supported jointly by the spring and by a stationary support, and a lighter spring results in less support provided by the spring and, consequently, more weight is supported by the stationary support resulting in greater friction between the impact disc and stationary support. As a lighter spring stores less energy for a particular amount of torsional deflection, a greater portion of the return energy is expended in overcoming the friction, thereby reducing the impact energy. Alternatively, utilization of a heavy spring requires a greater force from the water stream to deflect and rotate the impact arm and shortens the dwell time such that the full water stream pattern and throw may be unable to develop.
To improve dwell time, the mass of the impact disc assembly may be increased. However, an increase in mass requires greater water flow to energize, that is, to provide sufficient energy for acceleration and rotation of the impact disc. An increase in impact disc mass also requires a heavier spring, as described above. Accordingly, it has been found that variation of the mass of the impact disc assembly and corresponding variation of the spring constant of the spring generally correlate to balance the impact energy received.
Consequently, there has been a need for an improved impact sprinkler.